1. Field of the Invention
The invention relates to a process for the preparation of mixtures of light-colored bis(C.sub.8 -C.sub.22 -fatty acid) alkylenediamides and C.sub.8 -C.sub.22 -fatty acid esters and also, if desired, metal soaps of C.sub.8 -C.sub.22 -fatty acids.
2. Statement of Related Art
Bis(C.sub.8 -C.sub.18 -fatty acid) alkylenediamides, for example ethylenediamine distearate, are employed in the plastics industry as additives. They are used as slip agents, for example in the processing of rigid and plasticized PVC compositions, and impart excellent anti-block properties to the finished products, for example films. They are also suitable, however, for use as slip agents and mold release agents for plastics based on polystyrene. They are also employed in other thermoplastics, for example in the processing of polyesters and polyamides. In comparison with other slip agents and mold release agents they have high melting points (about 140.degree. C.). They therefore have no unfavorable effect on the heat distortion point of the plastics treated with them. By virtue of their properties, which can be assessed as physiologically acceptable, they are used for the preparation of PVC compositions for food packaging, pharmaceutical packaging, toys and medicinal tubing.
The starting materials for the bis(C.sub.8 -C.sub.22 -fatty acid) alkylenediamides, described below as fatty acid alkylenediamides, for example ethylenediamine or hexamethylenediamine, are very sensitive to oxidation at the reaction temperatures required for the reaction with fatty acids (about 170.degree. C.); the reaction with fatty acids is therefore expediently carried out under a protective gas or with the exclusion of air or oxygen. The fatty acid alkylenediamides are also similarly sensitive when they are used for making up by spraying or flaking. Normally, i.e. in the presence of air or oxygen, this results in discoloration, so that brown colored end products are obtained. Although it is also possible to convert fatty acid alkylenediamides into suitable made-up products of a small particle size by grinding, this is a labor-intensive and expensive measure.
For the reasons mentioned above, special equipment is required for the preparation of fatty acid alkylenediamides. It is not possible to carry out their preparation in an adequate quality in customary industrial equipment (esterification equipment or spray towers).